Disclosed are an expansion tool assembly, comprising: an expandable tubular; a guide shoe partially inserted into and connected to the lower end of the expandable tubular; a sealing sleeve arranged in the expandable tubular and connected to the upper end of the guide shoe; an expansion assembly comprising an expansion cone and expansion seat disposed inside the expandable tubular, wherein the lower end of the expansion seat is connected with hooks, which can be rested on the upper end of the sealing sleeve; an upper joint that is connected to the upper end of the expansion seat and can be connected to a drill string. A force transfer path can be established via connection between the expansion seat and sealing sleeve, so that expandable tubular weight is borne on the drill string. Unintentional expansion of the expandable tubular, caused by interaction between expandable tubular and expansion cone, can be avoided.